Re: Pondering per-process vsyscall disablement

On Fri, May 30, 2014 at 1:20 PM, H. Peter Anvin [off-list ref] wrote:

On 05/30/2014 01:11 PM, Andy Lutomirski wrote:

quoted

On Fri, May 30, 2014 at 1:05 PM, H. Peter Anvin [off-list ref] wrote:

quoted

On 05/30/2014 01:00 PM, Andy Lutomirski wrote:

quoted

Do the flags go in the ELF loader or in the executable we're running?
Or both (and, if both, do we and them or or them)?

I think the interpreter makes a little more sense in general: for the
most part, use of vsyscalls is a property of the runtime environment,
not of the program being run.  But maybe this is naive.

They go into each object which becomes part of the running program, i.e.
executable, dynamic libraries, and dynamic linker.

Well, sure, but the kernel is not about to start reading ELF headers
in dynamic libraries.  So we need to make a decision based on the
interpreter and the executable.  The conservative approach is to
require both to have the flag set *and* to offer a prctl to twiddle
the flags.  Then userspace loaders can do whatever they want, and
distros get to rebuild the world :)

Yes, something like that.

I'll hack something up once the merge window closes.  Or maybe sooner
if you commit my vsyscall patches from a few days ago.  Otherwise I'm
just going to confuse my git tree too much :)

--Andy

        -hpa


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Andy Lutomirski
AMA Capital Management, LLC